Problems of conformation, stereoselection and intermolecular interactions are key elements in both the understanding of the role of biologically important compounds, and in the design of their synthesis. The long term goal is to gain enough information concerning these problems so that more effective procedures for molecular modeling may be developed, and that non-covalent interactions between molecules may be better understood. The plan is to carry out both experimental and theoretical studies, and to relate the results of the two approaches in as detailed a fashion as possible. The problem of the factors determining stereo- and regioselection also will be examined. Specifically, it is proposed to determine the heats of formation of the C4-Cl2 monocyclic lactones vis calorimetric measurements and to study their conformations. These data will provide the first real test of current molecular mechanics force fields for lactones, and should allow better force fields to be developed. The acidity and basicity of lactones as a function of ring size also will be studied. In addition, non-covalent interactions will be studied making use of electrostatic potentials and related quantities. This is a commonly used model in a semiempirical sense. Detailed calculations of three dimensional electrostatic potential maps using large basis sets will be carried out, and will be related to models containing point charges, dipole and quadrupoles. The latter will be obtained from the wave functions. Other proposed studies include a study of regioselection in the ring opening of spirocyclic epoxides, and of epoxides having internal nucleophiles. Conformational studies will be continued for systems such as vinylacetaldehyde and phenylacetaldehyde.